Abstract: A modular pump assembly for pumping a viscous liquid, such as liquid manure. The viscous liquid is conveyed under pressure from an admission line to an evacuation line. The assembly has a base between the admission and evacuation lines. The base receives and conveys the liquid manure. The base can also be partitioned into separate sections 14 or chambers, thereby increasing pumping capacity and efficiency. At least one pump is vertically mounted to the base, and operates in a receiving configuration for receiving the liquid manure, and a pumping configuration for pumping the liquid manure. The inlet and out of the base are adjacent or coterminous with either another pump's inlet and outlet, or with another assembly, thereby allowing a pressurized flow of liquid manure through multiples pumps and/or assemblies arranged in series.